A Multi-Qubit Quantum Gate Using the Zeno Effect

TL;DR

This paper introduces a novel multi-qubit entangling gate based on the quantum Zeno effect, which uses measurement-induced dynamics to generate geometric phases for quantum computing in circuit and cavity QED systems.

Contribution

It demonstrates how the Zeno effect can be harnessed to create multi-qubit gates from non-interacting systems with single-qubit control, providing explicit fidelity expressions and implementation conditions.

Findings

The Zeno gate can generate entanglement via geometric phases.

Gate fidelity expressions are derived for various non-idealities.

Implementation conditions are established for circuit and cavity QED systems.

Abstract

The Zeno effect, in which repeated observation freezes the dynamics of a quantum system, stands as an iconic oddity of quantum mechanics. When a measurement is unable to distinguish between states in a subspace, the dynamics within that subspace can be profoundly altered, leading to non-trivial behavior. Here we show that such a measurement can turn a non-interacting system with only single-qubit control into a two- or multi-qubit entangling gate, which we call a Zeno gate. The gate works by imparting a geometric phase on the system, conditioned on it lying within a particular nonlocal subspace. We derive simple closed-form expressions for the gate fidelity under a number of non-idealities and show that the gate is viable for implementation in circuit and cavity QED systems. More specifically, we illustrate the functioning of the gate via dispersive readout in both the Markovian and non-Markovian readout regimes, and derive conditions for longitudinal readout to ideally realize the gate.